As one of the methods for controlling internal combustion engines for automobiles, there is known torque demand control that determines a manipulated variable of an actuator with a torque as a controlled variable. Torque demand control also can be applied to internal combustion engines with turbo superchargers. In the torque demand control of an internal combustion engine with a turbo supercharger, a manipulated variable of a throttle is determined based on a requested torque, and a manipulated variable of an actuator for supercharge pressure control is determined based on the requested torque. A supercharge pressure controlling actuator is an actuator that can actively control a rotational frequency of a turbine, and a wastegate valve and a variable nozzle can be cited as examples. In more detail, the operation of the supercharge pressure controlling actuators is performed in accordance with a target supercharge pressure determined based on the requested torque. As a method for determining the target supercharge pressure from the requested torque, there is known a method that determines a target air amount from a requested torque, and further calculates a target supercharge pressure from the target air amount, as disclosed in Japanese Patent Laid-Open No. 2007-315217. Further, there is also known a method that determines a target intake pressure from a target air amount, and calculates a target supercharge pressure from the target intake pressure, as disclosed in Japanese Patent Laid-Open No. 2006-152821.
In the torque demand control for an internal combustion engine with a turbo supercharger, a target supercharge pressure is determined with emphasis placed on operation performance, in more detail, response of a torque generated by the internal combustion engine to an accelerator operation. However, the performance required of an internal combustion engine is not only the operation performance like this. Exhaust gas performance, namely, reducing harmful components contained in an exhaust gas is also one of the performance required of an internal combustion engine. Besides obtaining sufficient exhaust gas performance, activating an exhaust gas purifying catalyst early is one requirement, and for this purpose, warming-up of the exhaust gas purifying catalyst has to be performed quickly. However, in the case of an internal combustion engine with a turbo supercharger, an exhaust gas temperature is sometimes reduced due to heat loss that occurs in the turbine. In order to increase a supercharge pressure, large turbine work is necessary, but as the turbine work is larger, the heat loss occurring in the turbine becomes larger. Therefore, depending on the method for controlling the supercharge pressure, there arises the fear of interfering warming-up of the exhaust gas purifying catalyst due to reduction in the exhaust gas temperature in the turbine.